LMC1982 National Semiconductor, LMC1982 Datasheet - Page 7

• Manufacturer Part Number: LMC1982
• Description: Digitally-Controlled Stereo Tone and Volume Circuit with Two Selectable Stereo Inputs
• Manufacturer: National Semiconductor

Pin Description
General Information
The LMC1982 is a CMOS/bipolar building block intended for
high fidelity audio signal processing. It is designed for line
level inputs signals (300 mV − 2V) and has a maximum gain
of −0.5 dB. While the LMC1982 is manufactured with CMOS
processing, NPN transistors are used to build low noise op
amps. The combination of CMOS switches, bipolar op amps,
and poly-silicon resistors make it possible to achieve an or-
der of magnitude quality improvement over other bipolar cir-
cuits that use analog multipliers to accomplish gain adjust-
ment. Internal circuits set the volume to minimum, tone
controls to flat, the mute to on, and all other functions off
01000000
01000001
01000010
01000011
01000100
01000101
01000110
01000111
Address
(A7–A0)
(Continued)
Loudness, Enhanced Stereo
TABLE 1. IM Bus Programming Codes for LMC1982
Read Digital Input 1
Input Select + Mute
Digital Input 2
Right Volume
Mode Select
Left Volume
on IM Bus
Function
Treble
Bass
or
7
when power is first applied. Individual left and right volume
controls are software programmed to achieve the stereo bal-
ance function. Figure 1 shows the connection diagram of a
typical LMC1982 application.
The LMC1982 has internal decoding logic that allows a mi-
croprocessor (µP) or microcontroller (µC) to communicate di-
rectly to the audio control circuitry through an INTERMETAL
(IM) Bus interface. This three-wire interface consists of a
bi-directional DATA line, a Clock (CLK) input line, and an
Identity (ID) line. Address and function selection data (8 bits)
XXXXXXD1D0
XXXXXX00
XXXXXX01
XXXXXX10
XXXXXX11
XXXXXX00
XXXXXX01
XXXXXX10
XXXXXX11
XXXX11XX
XXXX11XX
XX101XXX
XX11XXXX
XX101XXX
XX11XXXX
XXXXX100
XXXXX101
XXXXX11X
XXXX0000
XXXX0011
XXXX0110
XXXX1001
XXXX0000
XXXX0011
XXXX0110
XXXX1001
XX000000
XX000000
XX010100
XX010100
Data
Enhanced Stereo OFF
Enhanced Stereo OFF
Enhanced Stereo ON
Enhanced Stereo ON
D0 = Digital Input 1
D1 = Digital Input 2
Loudness OFF
Loudness OFF
Loudness ON
Loudness ON
Right Mono
Left Mono
Function
Selected
INPUT1
INPUT2
−12 dB
+12 dB
−12 dB
+12 dB
−40 dB
−80 dB
−80 dB
−40 dB
−80 dB
−80 dB
Stereo
MUTE
−6 dB
+6 dB
−6 dB
+6 dB
FLAT
FLAT
0 dB
0 dB
N/A
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